Reliability, construct validity, and measurement invariance of the PROMIS Physical Function 8b-Adult Short Form v2.0

The National Institutes of Health established the Patient-Reported Outcomes Measurement Information System (PROMIS) to assess health across various chronic illnesses. The standardized PROMIS measures have been used to assess symptoms in studies that included Native American participants, although the psychometric properties of these measures have not been assessed among a solely Native American population. This study aimed to assess the reliability, construct validity, and measurement invariance of a widely used PROMIS Physical Function survey among Native Americans residing on or near the Apsáalooke (Crow) Reservation who were living with chronic illnesses.

Participants aged 24 to 82 years and living with at least one chronic illness were recruited for a community-based participatory research project. Baseline data were used for the current study (N = 210). The 8-item PROMIS Physical Function 8b-Adult Short Form v2.0 was used to assess the function of upper and lower extremities, central core regions, and the ability to complete daily activities on a 5-point Likert scale.

Results indicated that the above PROMIS survey had high internal consistency (Cronbach's α = 0.95) and split-half (r = 0.92, p < 0.001) reliabilities. Confirmatory factor analyses supported construct validity among females of the above population and when the two sex groups were combined. Results also indicated that corresponding thresholds and factor loadings were invariant across male and female groups.

The above PROMIS measure had good psychometric properties in females and when the two sex groups were combined among Native American adults living on or near the Apsáalooke reservation with chronic illnesses. Thresholds and factor loadings appeared to be invariant by sex. Future studies with a larger sample size among males and more studies on the psychometric properties of other PROMIS measures among Native American populations are needed.